1. Field of the Invention
The present invention relates to image sensor arrays. More particularly, the present invention relates to CMOS storage pixel sensors and arrays for applications such as still cameras and to methods for operating those sensors and arrays.
2. The Prior Art
Integrated image sensors are known in the art. Such sensors have been fabricated from charge-coupled devices (CCDs) and as bipolar and MOS image sensors.
Storage pixel sensors formed from MOS devices are known in the art. MOS storage pixel sensors employ capacitive storage elements. One such storage pixel sensor and array is disclosed in co-pending application Ser. No. 08/969,383, filed Nov. 13, 1997, entitled INTRA-PIXEL FRAME STORAGE ELEMENT, ARRAY, AND ELECTRONIC SHUTTER METHOD SUITABLE FOR ELECTRONIC STILL CAMERA APPLICATIONS, assigned to the same assignee as the present invention.
It is a delicate task to select a satisfactory capacitor value for MOS storage pixel sensors. For good photocharge to voltage gain in the storage pixel sensor, it is desirable to employ a small capacitance. If the capacitor value is too small, however, the storage time of the pixel sensor suffers because the voltage on the small storage capacitance is easily subject to change by mechanisms such as dark current. For good storage integrity, it is desirable to employ a larger capacitor. If the capacitor value is too large, however, the photocharge generated by the photosensor element in the pixel sensor does not cause much of a voltage change on the capacitor during integration of photocharge.
It is therefore an object of the present invention to provide a storage pixel sensor and an array of pixel sensors that overcome some of the shortcomings of the prior art.
A further object of the present invention is to provide a storage-pixel sensor and an imaging array of storage-pixel sensors that provides good photocharge-to-voltage gain.
Another object of the present invention is to provide a storage-pixel sensor and an imaging array of storage-pixel sensors that provides good voltage stability during a storage period.
Yet other object of the present invention is to provide a storage-pixel sensor and an imaging array of storage-pixel sensors that provides good photocharge-to-voltage gain and that provides good voltage stability during a storage period.